STING (stimulator of interferon genes) is a signaling molecule in the innate response to dsDNA in the cytosol. STING deletion has been reported in multiple human cancers. In addition, deregulation of STING signaling in human cancers also has been reported in melanoma (Xia T, et al., “Recurrent Loss of STING Signaling in Melanoma Correlates with Susceptibility to Viral Oncolysis” Cancer Res. 2016) and colon cancer. (Xia T, et al., “Deregulation of STING Signaling in Colorectal Carcinoma Constrains DNA Damage Responses and Correlates With Tumorigenesis” Cell Rep. 2016; 14:282-97). Interestingly, in those studies, genomic analysis results showed loss expression of STING is not due to gene deletion or mutation, but through epigenetic changes. (Xia, Cancer Res. 2016; Xia, Cell Rep. 2016). STING's cancer protection activity is also supported by evidence obtained from mouse model studies. STING knockout mice have shown defective tumor control. (Woo S R, et al. “STING-dependent cytosolic DNA sensing mediates innate immune recognition of immunogenic tumors” Immunity 2014; 41:830-42).
In addition, STING's role in protecting ontogenesis has been demonstrated in several mouse spontaneous models, including glioma (Ohkuri T, et al., “Protective role of STING against gliomagenesis: Rational use of STING agonist in anti-glioma immunotherapy” Oncoimmunology. 2015; 4:e999523), and colon cancer (Zhu Q, et al., “Cutting edge: STING mediates protection against colorectal tumorigenesis by governing the magnitude of intestinal inflammation” J. Immunol. 2014; 193:4779-82). This anti-tumor effect may be due to its ability to counter over-activation of NF-kB and STAT3. (Okihuri 2015). Activation of STING pathway also showed potent activity in preclinical mouse tumor models. (Woo 2014; Chandra D, et al. “STING ligand c-di-GMP improves cancer vaccination against metastatic breast cancer” Cancer Immunol Res. 2014; 2:901-10; Corrales L, et al., “Direct Activation of STING in the Tumor Microenvironment Leads to Potent and Systemic Tumor Regression and Immunity” Cell Rep. 2015; 11:1018-30; Curran E, et al. “STING Pathway Activation Stimulates Potent Immunity against Acute Myeloid Leukemia” Cell Rep. 2016; 15:2357-66; Tang C H, et al. “Agonist-Mediated Activation of STING Induces Apoptosis in Malignant B Cells” Cancer Res. 2016; 76:2137-52). This anti-tumor activity is likely due to disruption of tumor vasculature and followed by induction of adaptive immune response. (Corrales L, et al., “The host STING pathway at the interface of cancer and immunity” J. Clin. Invest. 2016; 126:2404-11). Accordingly, direct stimulation of STING in a tumor microenvironment by an agonist may represent a novel approach for treating multiple cancer types.